FIG. 1A illustrates a conventional harvester or combine 10. As the operator in cab 12 drives the combine 10 through the field, the crop being harvested is drawn through the header 15 which gathers the plant material and feeds it into the feederhouse 16. The feederhouse 16 carries the plant material into the combine where the grain is separated from the other plant material. The separated grain is then carried upward by the grain elevator 120 (FIG. 1B) to the fountain auger 150 which carries the grain into the grain tank 20. The other plant material is discharged out the back of the combine.
When the grain tank 20 becomes full, a transport vehicle such as grain cart, wagon or truck is driven up next to the combine or the combine drives to the awaiting transport vehicle. The unloading auger 30 is swung outwardly until the end is positioned over the awaiting transport vehicle. A cross-auger 35 positioned in the bottom of the grain tank 20 feeds the grain to the extended unloading auger 30 which in turn deposits the grain into the awaiting transport vehicle below.
Live or real-time yield monitoring during crop harvesting is known in the art. One type of commercially available yield monitor uses a mass flow sensor such as mass flow sensor 130 illustrated in FIG. 1B and as disclosed in U.S. Pat. No. 5,343,761, which is hereby incorporated herein in its entirety by reference. Referring to FIG. 1B, as the grain 110 is discharged from the elevator 120 it strikes an impact plate 140. Sensors associated with the mass flow sensor 130 produce a voltage related to the force imposed on the impact plate 140. The volumetric flow of grain can then be calculated based on the voltage such that the mass flow sensor 130 determines a grain flow rate associated with grain within the combine 10. Such systems also employ various methods of recording the speed of the combine in operation. Using the speed and the width of the pass being harvested (usually the width of the header), it is possible to obtain a yield rate in bushels per acre by dividing the mass of grain harvested over a particular time period by the area harvested. In addition to reporting the current yield rate, such systems often incorporate GPS or other positioning systems in order to associate each reported yield rate with a discrete location in the field. Thus a yield map may be generated for reference in subsequent seasons.
Most commercially available systems also utilize a sensor to determine the moisture of the grain as it is being harvested. Sensing the grain moisture permits the operator to determine the likely time or expense required to dry the harvested crop and it also allows the yield monitor to report more useful yield data by correcting for water content. Because grain is dried before long-term storage and sale (e.g., to an industry-standard 15.5% moisture), the as-harvested moisture level can be used to calculate the weight of saleable grain per acre.
While harvesting, various factors affect the reliability of the mass flow sensor. Changes in crop yield, grain type, seed variety and genetics, grain moisture, and ambient temperature are known to change the flow characteristics of the grain and thus change the signal produced by the sensor for the same mass flow rate. Due to these changing conditions during operation, it is well known that mass flow sensors may be inaccurate without proper calibration.
For this reason, manuals provided with commercially available yield monitors generally instruct the operator to occasionally carry out a calibration routine. Most commonly, when a load of grain is unloaded into a weigh wagon or scale, the operator enters the measured weight of grain, and the yield monitor system applies a correction factor to its signal by comparing the measured weight with its calculated accumulation of mass.
One of several disadvantages of this load-by-load calibration method is that it is time-consuming and is often simply not performed on a regular basis by the operator. Recognizing that many producers do not perform regular calibrations and in an attempt to automate the calibration process, some grain carts have been adapted to wirelessly transmit the load weight to the yield monitor system, as disclosed in U.S. Pat. No. 7,073,314 to Beck et al. However, where multiple grain carts are used, this method requires instrumentation of additional machines in order to obtain a load-by-load calibration, and no calibration is likely feasible when the operator offloads grain directly into a grain truck. Additionally, load-by-load calibration may not be possible when, for example, the grain tank can only be partially unloaded. Moreover, this method does not eliminate the inherent defects of load-by-load calibration discussed below.
Even if the operator or yield monitor system regularly performed a calibration routine, many of the conditions that affect the mass flow sensor change numerous times throughout accumulation of each load such that the calibration routine is unable to correct for such changes. Put another way, the various changes in conditions that require mass flow sensor correction will rarely coincide with a load-by-load calibration schedule. For example, a load of high-moisture grain may be harvested and used to recalibrate the mass flow sensor just before entering a drier area of the field, causing the mass flow sensors to be more inaccurate than if no calibration had been performed.
As such, there is a need for a system and method of accurately calibrating the mass flow rate sensor of a yield monitor while harvesting.